Researchers examined data on more than 238,000 women who participated in the
Nurses' Health Study, which began in 1976, and the Nurses' Health Study II,
which began in 1989. Participants self-reported what their height and weight
were at the start of the study and what they had been at age 18. They also
chose silhouettes to describe their body shapes when they were ages 5, 10, and
20 years old. Participants were between 25 and 55 years old when the studies
began.

The study tracked participants for more than 40 years from both groups
combined. During that time there were 593 cases of MS.

The women's body mass index (BMI) at age 18 and the way they described their
overall body shape at age 20 were linked to the likelihood of developing MS in
adulthood. Women who had a BMI of 30 or larger (considered obese) at age 18 had
more than twice the risk of women with a BMI between 18.5 and 20.9. Normal
weight BMI is 18.5 to 24.9.

The results were the same after accounting for factors such as smoking
status, age, and ethnicity.

There also was a link between the women who chose a larger silhouette to
describe themselves at age 20 and an increased risk for MS.

Being obese as determined by the BMI at the start of each study was not
linked to likelihood of MS. Body silhouette self-selected at age 5 also wasn't
linked to risk for developing MS later in adulthood.

"Our results suggest that weight during adolescence, rather than childhood
or adulthood, is critical in determining the risk of MS," study researcher
Kassandra Munger, ScD, of Harvard School of Public Health, says in a news
release. "Teaching and practicing obesity prevention from the start, but
especially during teenage years, may be an important step in reducing the risk
of MS later in life for women."